1. Technical Field
The present invention relates to detectors in elevators and, more particularly, to the detection of obstructions in an elevator car doorway.
2. Background Art
In elevators, it is common to use one or more automatic sliding doors. Systems are used to detect the presence of an obstruction within the door opening before and during closure for the protection of the passengers. If the system detects an obstruction, the elevator doors are prevented from closing further and preferably are reopened.
One known system for detecting obstructions in the path of elevator doors places light beams in a path across the door opening and uses a sensor to detect an interruption of the light beams, which occurs if an obstruction is disposed within the door opening. Upon sensing the interruption, the sensor issues a signal to alter the motion of the doors, and preferably reopen them.
The system has an array of light emitters disposed vertically on one side of the door, producing light beams, and a corresponding array of photo-sensitive detectors arranged on the other door, for sensing those light beams, thus creating a system which can sense obstructions at different heights in the doorway. The emitters and detectors are disposed on the doors such that if the doors are open then the emitters and detectors are far apart and if the doors are closed, or closing, the emitters and detectors are in close proximity.
The amplitude of the light beam is related to the distance it has to travel between the emitters and the detectors; more specifically, the farther the beams must travel, the greater the beam amplitude must be in order to achieve proper detection of the beams by the detectors. As a result, the system requires a high beam amplitude when the doors are open and far apart.